This invention relates generally to improvements in turbochargers of the type used to provide pressurized air to an internal combustion engine. More particularly, this invention relates to a turbine housing assembly designed for improved cooling of metal portions exposed to hot engine exhaust gases and having a wastegate valve and a bypass passage which cooperate to provide an efficient exhaust ejector to reduce backpressure on the engine.
Turbochargers in general are well known in the art for supplying relatively high pressure air, commonly referred to as charge air, to the intake manifold of an internal combustion engine such as a reciprocating piston engine of the type commonly used to power automobiles, trucks, buses, and the like. Typically, the turbocharger comprises a turbine housing connected for receiving exhaust gases expelled from the engine and configured for guiding those exhaust gases into driving communication with a rotatable turbine wheel. The turbine wheel is carried by a rotatable shaft commonly connected to a compressor impeller within a compressor housing. The turbine wheel thus rotatably drives the impeller which in turn draws ambient air into the compressor housing for compression and discharge in the form of charge air for supply to the intake manifold of the engine.
Turbocharged engines are highly advantageous when compared with conventional naturally aspirated engines in that substantially denser air is delivered to the combustion chamber or cylinders of the engine. This increased air density, or mass, permits the engine to be operated at substantially increased levels of performance and power output, and frequently with greater efficiency. However, with many combustion engines, it is desirable to control operation of the turbocharger so that the charge air is supplied to the engine only on demand and at a pressure level not exceeding predetermined design limits. In this regard, a variety of control schemes are known such as, for example, the provision of a bypass passage for nondriving bypass flow of a portion of the exhaust gases around the turbine wheel in combination with a so-called wastegate valve for opening and closing the bypass passage in response to selected engine parameters. For examples of wastegate valve control schemes, see U.S. Pat. Nos. 3,035,408; 4,120,156; 4,177,006; 4,251,050; and 4,256,019.
In most turbochargers, particularly of the type used with relatively small automobile engines, it is highly desirable to minimize the number of component parts in order to reduce overall manufacturing and material cost. In this regard, it is known to form the turbine housing of the turbocharger from a single component, typically a metal casting, to include an inlet passage for receiving exhaust gases, a volute passage for communicating the exhaust gases to a turbine wheel, an exducer passage through which the exhaust gases are discharged, and the bypass passage communicating between the inlet and exducer passages. These various passages are defined, for the most part, by metal surfaces exposed on one side to the hot exhaust gases and on the other side to ambient air which tends to cool the housing sufficiently to prevent heat degradation of the metal. However, in a unitarily cast turbine housing of this type, a relatively small region of metal separating the bypass passage from the volute and exducer passages is surrounded at all times by hot exhaust gases, whereby this region of metal has been found to degrade quickly from exposure to heat.
In addition to the foregoing, an inherent disadvantage arising from use of a turbocharger with a combustion engine is that the turbocharger necessarily restricts passage of the exhaust gases expelled from the engine and thereby results in an increase in backpressure or load acting upon the engine. This increase in backpressure is present for all conditions of engine operation since at least some of the exhaust gases flow into driving communication with the turbine wheel even when the wastegate valve is fully open. This backpressure can adversely affect engine performance particularly when the wastegate valve is open and it is desired to operate the engine in a normal unboosted mode.
Some turbocharger systems have been proposed seeking to minimize the adverse effects of increased backpressure acting upon the engine. See, for example, U.S. Pat. No. 3,104,520 wherein a bypass passage is oriented for flow of exhaust gases in a downstream direction within a turbine outlet passage. When a wastegate valve is opened, the bypassed gas flow provides a so-called fluid ejector creating a localized region of decreased fluid pressure at the downstream side of the turbine, wherein this decreased fluid pressure advantageously draws gases through the turbine housing to result in a reduction in backpressure acting upon the engine. While systems of this general type offer improvements over conventional wastegate valve schemes, they have not optimized the fluid ejector design, particularly with regard to the wastegate valve which impedes gas flow through the bypass passage.
The present invention overcomes the above-described problems and disadvantages by providing an improved turbocharger turbine housing assembly including a wastegate valve and bypass passage designed to form an efficient fluid ejector wherein the wastegate valve does not restrict or impede exhaust gas flow and further including an air vent for improved cooling of the portion of the turbine housing between the bypass and the exducer passages.